import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JButton;
import java.awt.BorderLayout;
import java.awt.FlowLayout;
import java.awt.GridLayout;
import java.awt.Color;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class PanelDemo extends JFrame implements ActionListener{

    public static final int WIDTH = 300;
    public static final int HEIGHT = 200;

    private JPanel greenPanel;
    private JPanel whitePanel;
    private JPanel grayPanel;

    public static void main(String[] args)
    {
        PanelDemo gui = new PanelDemo();
        gui.setVisible(true);

    }

    public PanelDemo()
    {

        super("Panel Demonstration");
        setSize(WIDTH, HEIGHT);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLayout(new BorderLayout());

        JPanel biggerPanel = new JPanel();
        biggerPanel.setLayout(new GridLayout(1, 3));

        greenPanel = new JPanel();
        greenPanel.setBackground(Color.LIGHT_GRAY);
        biggerPanel.add(greenPanel);

        whitePanel = new JPanel();
        whitePanel.setBackground(Color.LIGHT_GRAY);
        biggerPanel.add(whitePanel);
        grayPanel = new JPanel();
        grayPanel.setBackground(Color.LIGHT_GRAY);
        biggerPanel.add(grayPanel);

        add(biggerPanel, BorderLayout.CENTER);

        JPanel buttonPanel = new JPanel();
        buttonPanel.setBackground(Color.LIGHT_GRAY);
        buttonPanel.setLayout(new FlowLayout());

        JButton greenButton = new JButton("Green");
        greenButton.setBackground(Color.GREEN);
        greenButton.addActionListener(this);
        buttonPanel.add(greenButton);

        JButton whiteButton = new JButton("White");
        whiteButton.setBackground(Color.WHITE);
        whiteButton.addActionListener(this);
        buttonPanel.add(whiteButton);

        JButton grayButton = new JButton("GRAY");
        grayButton.setBackground(Color.GRAY);
        grayButton.addActionListener(this);
        buttonPanel.add(grayButton);

        add(buttonPanel, BorderLayout.SOUTH);

    }

    public void actionPerformed(ActionEvent e)
    {
        String buttonString = e.getActionCommand();

        if (buttonString.equals("Green"))
            greenPanel.setBackground(Color.GREEN);

        else if (buttonString.equals("White"))
        {
            whitePanel.setBackground(Color.WHITE);
        }
        else if (buttonString.equals("Gray"))
        {
            grayPanel.setBackground(Color.GRAY);
        }
        else
            {
            System.out.println("Unexpected error.");
            }

            }
    }
}